Backlash remover



May 28, 1935. c. B. DE VLIEG BACKLASH REMOVER Original Filed Nov. 1,1928 Patented May 28, 1935 BACKLASH REMOVER Charles B. De Vlies,Jackson, Mich., assignor to 'Associated Patents, Inc., Cincinnati, Ohio,a

corporation 01 Ohio Refiled for abandoned application Serial No.316,504, November 1, 1928. This application October 31, 1932, Serial No.640,561

19 Claims.

This is a substitute for my application for back lash remover filedNovember 1, 1928, Serial No. 316,504.-

The object of this invention is to provide a back lash remover inconnection with a screw and nut feed wherever applicable.

The invention is also an improvement in machine tools for removing oreliminating back lash in connection with the table movement, the objectbeing to provide a solid abutment against which the cutting load thrustis taken under conditions such as are illustrated herein.

In the present case my invention when applied to a milling machineprovides for the removal or elimination of back lash in the table feedwhen the direction of cutting is reversed from normal cutting forperforming what is known as climb cutting. Climb cutting occurs when thework piece is fed into the cutter in the same direction as the travel ofthe cutter teeth. Under such condition without my invention the resultwould be a more or less intermittent feed with the work piece feedinginto the cutter until the cutter tooth took an excessive and usuallydestructive thickness of chip which would advance the table to the endof any back lash between the feed screw and the nut. This not onlyproduces defective milling but is destructive of the cutter and themechanism in general. My invention provides a table movement that willbe positive and without back lash at all times, so that it is possibleto mill with a feed operating in each direction and the cutter rotatingin one direction or in either of the two directions of rotation.

Heretofore, machines have been designed to avoid the conditionsproducing the objections and disadvantages noted but, so far as I amaware, they comprise more or less complicated mechanisms which areobjectionable both because of 40 the additional cost and the lack ofrigidity and accuracy due to the many wearing parts, also because theycannot be operated in both directions of rotation of the screw or nutdriving element as the case may be, or because they have a transitoryinterval or period of inoperativeness to perform the function of thisinvention. The present invention is, therefore, not only of generalapplication to screw and nut feeds, but is an improvement in the art ofmilling machines for the reason that it allows conventional cutting inone direction and climb cutting in the reverse direction of travel ofthe work table without the disadvantages heretofore experienced.

I have also aimed to provide a simple and mode of operation adapted forapplication to any machine tool having a screw and a. nut feed.

Other objects and attendant advantages will be appreciated bythose'skilled in this art as the invention becomes better understood byref- 5 erence to the following description when considered in connectionwith the accompanying drawing, in which- Figure 1 is a front elevationpartly in vertical section of a milling machine to which my in- 10vention is applied;

Fig. 2 is an enlarged vertical section through the screw and nut tablefeed mechanism and parts in which my improvements are centered;

Fig. 3 is a cross-section taken substantially on 15 the line 33 of Fig.2, and

Fig. 4 is a fragmentary section taken substantially on the line 4-4 ofFig. 2.

My invention may be applied to any screw and nut feed where the problemis to provide a positive table or carriage movement without back lashunder all conditions of operation. In the present illustration, myinvention is applied to a case wherein the feed is in oppositedirections and the cutting thrust is in a. single direction. 25 In thiscase, the invention is applied to a milling machine having a work table5 mounted for reciprocation on the bed 6 and a milling cutter I attachedto a spindle 8 which in turn is mounted for rotation on a horizontalaxis in a head 9. 30 Suitable mechanism (not shown) rotates the cutterspindle in a counter-clockwise direction only. The cutter is adapted tomill work pieces II) and II at both ends of the table by feed of thetable in opposite directions. With my invention the table movement willbe positive and without the troubles incidental to back lash, as will bepresently apparent. It is not necessary, of course, that the cuttershall operate upon two work pieces, since in some cases the cutting maybe in opposite directions on a single work piece, or at a single stationfor climb cutting only.

The cutter preferably rotates continuously in the direction indicatedwhile the machine is in operation. The table is propelled by a screw l2which operates in a nut l3 fixed to the bed 6. The screw has a suitableanti-friction thrust bearing connection at H in an arm l5 fixed to oneend of the table. By rotating the screw in opposite directions as bymeans of a double gear I 8 having a key spline connection with screw andsuitable drive gears l1 and I8, the table will be fed back and forth,the screw translating with the table.

Referring now to Fig. '2, it will be apparent that when the screw isrotated to feed the work piece III to the left into the cutter, thethrust of the screw thread is against the side IQ of the thread of thefixed nut l3. The thrust is against the same side of the thread bothwhen the table is being propelled in this direction as for rapidtraverse to the cutter and when carrying the full load of the cutterresistance when feeding. This is the normal milling operation and iscommon practice in most milling machines. The load is directly againstthe side I9 of the nut thread, and because of the well known wedge likecutting action of the cutter teeth, the feed is positive and withoutback lash troubles. However, as soon as the direction of the table isreversed with a machine of this kind prior to my invention the thrust ofthe screw in propelling the table is transferred against the side 20 ofthe nut thread, and as soon as the work piece II is fed into the cutter(rotating in the same direction as in the case of said normal milling) adifferent cutting action takes place commonly termed climb cutting inwhich the cutter exerts a force throwing the screw thread against theopposite face IQ of the fixed nut thread to the extent of the existingplay or clearance between these parts. Such play or back lash, howeversmall, in the screw and the nut connection will have a decidedlyobjectionable effect on the cutting and a destructive effect on thecutter. The tendency of each cutter tooth will be to take an excessiveand usually-destructive bite or thickness of chip and to advance thetable to the end of the back lash. This produces an intermittent,irregular, jumping feed as'is well known in this art.

My invention overcomes the objections noted by the provision of meansfor exerting a force against the screw to always cause its thread tobear against the side I! of the fixed nut thread, thus removing any playor back lash and providing a solid abutment at all times for the thrustof the screw. This is accomplished in the present instance by theprovision of a supplemental nut 2| on the screw and suitable means forcausing the nut to exert said force in a common direction against thescrew when the latter is rotated in either direction. Said means in thisembodiment comprises a coiled spring 22 compressed between a. normallyfixed but adjustable abutment 23 and a. rack member 24 meshing withteeth on the periphery of the supplemental nut 2|. The parts 2|, 22, 23and 24 are mounted in a suitable housing 25 fixed with respect to thebed of the machine. The supplemental nut has a serrated face 26 in thenature of multiple cams engaging a similarly serrated face 21 fixed tothe housing 25. It will be seen that the spring-operated rack causes thesupplemental nut to turn in a clockwise direction viewing Fig. 3 tocause the screw to bear against the side l9 and thread of the fixed nut.There is also a cam action'of the nut cam face 26 against the fixed camface 21. The effect of this construction is to produce a spring-operatedwedge forcing the screw against the desired side of the fixed nut in asemi-solid manner without excessive spring pressure on the screw itselfand still such as will yield to variance in the pitch diameter of thescrew as well as to variance caused by wear. This force against thescrew is greater than the load of moving the table in the rapid traverseor feed thereof to the right to bring the work piece II to the cutter,with the result that the supplemental nut serves to maintain the screwagainst the side IQ of the fixed nut when climb out feeding, traversingor rapid approaching the table to the right. Consequently, when thecutter enters the work piece there is no back lash and in fact the loador thrust is at all times against a solid abutment, that is, the side I9of the fixed nut. When feeding in this direction the force of the cutteragainst the work piece by reason of the climb cutting is so great as totend to force the table and the screw ahead. In other words, the tablepropelling force is derived from the cutter rather than from the screw.As a result of this action the screw thread is forced against the sideIQ of the fixed nut, the screw serving merely as a metering mediumregulating the feed. Thus the screw has a solid abutment against thefixed nut at all times and especially during the reverse feed, therebyresisting the climbing tendency of the cutter and permitting it to takeonly its normal thickness of chip.

The removal of back lash in this manner also serves to permit climbcutting in either direction with a single piece of work and a cutterrotation of either direction. It also permits the .use of two sets ofcutters mounted on the spindle set up for opposite directions of cuttingaction. This is desirable with two work pieces in staggered positionrelative to the cutter location and by means of a reversing spindledrive the pronounced advantage of climb cutting on each work piece isobtained. In this instance the abutment for the cutting thrust in onedirection is taken against the side of the screw indicated at l9, and inthe opposite direction on the auxiliary nut against the outside of thethread shown at 20.

One of the features of my invention exemplified in the embodiment hereinillustrated is the use of means serving as a pressure wedge. constantlyexerting pressure axially between the nut elements, the angle of thewedge serving to cause one of the nut elements to constantly take upwear of 'the threads in both nuts and yield to irregularities of thescrew thread, yet provide sufficient thrust between the motiontransmitting elements to maintain the screw thread against a common sideof the nut thread for either direction of motion transmission. Thisfeature of my invention is, I believe, distinctly new and is applicableto screw and nut transmissions wherever used. It is particularlyadvantageous and desirable for the movement of supports, tables orcarriages for either work pieces or tools.

Aside from the advantages above described in the application of myinvention to a milling machine it should be noted that the action of thepressure wedge referred to is a constantly functioning action regardlessof the direction of rotation of the driving element. This avoids periodsof non-functioning and makes for greater accuracy and precision in theoperation and control of the part to which motion is transmitted and isparticularly desirable as a. precision factor in machine tools. Apronounced advantage is derived from my invention as a measuring devicefor the accurate positioning or feeding of a carriage table or the like.It provides the advantage of a pre-loaded and constant pressure againstone side of the screw and eliminates the very small but objectionablevariables introduced by oil films and other conditions when no provisionis made for uniform and adequate pressure against the one side of thescrew.

It is believed that the principles of my invention will be readilyunderstood by those skilled in this art and, while I have for purpose ofillustration shown but a single embodiment as applied to amillingmachine it will be apparent from the above disclosure and descriptionthat my invention is applicable wherever screw and nut transmissionelements are employed, particularly in machine tools.

I claim:

1. In a machine tool, the combination of a cutting tool, a reciprocablework table, a fixed nut, a screw in said nut connected to the table,means for rotating the screw in opposite directions, a

supplemental nut on the screw, gear teeth on the periphery of saidsupplemental nut, a toothed member meshing with said gear teeth, acoiled spring acting between said tooth member and a fixed membertending to impart rotative movement to the supplemental nut, a camsurface on said supplemental nut, and a fixed cam surface against whichthe cam surface on the nut acts, whereby to produce a force actingagainst the screw for maintaining its thread against one side of thefixed nut thread.

2. In a milling machine, the combination of a milling cutter, a worksupport, a screw member and a nut member, one of which is adapted to berotated in opposite directions to produce feed movement'between themilling cutter and the work support in opposite directions, the millingcutter being rotated in one direction only for milling work in oppositedirections for normal milling and climb milling, respectively, asupplemental nut on the screw member, means constantly imparting a force'rotatively against the supplemental nut, and cam faces acted on byrotation of said supplemental nut for exerting a force against the screwmember to cause its thread to bear against one side only of the threadof the nut member at all times when feeding in opposite directions andwhen reversing from one direction to the other, whereby the screw ismaintained against said one side only of the thread of the nut memberboth when normal milling and climb milling.

3. In a milling machine, the combination set forth in claim 2, includingmeans providing for rotative yielding movement of the supplemental nutwhile exerting said force to accommodate variances in pitch diameter ofthe screw member.

4. In a milling machine, the combination of a milling cutter, areciprocable work table, a screw connected to the table forreciprocating the same,

a fixed nut in which the screw turns, means for rotating the screw inone direction for feeding the work table for normal milling and in theopposite direction for climb milling, a fixed member having an inclinedface, a supplemental nut on the screw having end thrust in one directionagainst said inclined face of said fixed member, means for. imparting aforce rotatively against the supplemental nut in a direction to turn iton the screw with the thrust against said inclined surface whereby toexert a force against the screw for maintaining its thread against oneside of the thread of the fixed nut both when normal and climb milling.

5. In a milling machine, the combination of a frame, a rotary millingcutter supported on the frame, a work table supported on the frame forreciprocation in a plane at right angles to the axis of rotation of themilling cutter, a screw member connected to the work table, a nut memberon the screw, means for rotating one of said members to propel the worktable in feed move ments in both directions, the nut member beingsupported on the frame in such manner as to take the'end thrust frompropelling the work table as well as the thrust from the millingoperations, the milling cutter being, rotated only in one directionwhereby to produce normal milling when the work table is propelled inone direction and climb milling when propelled in .the oppositedirection, a supplemental nut on the.screw, a member against which thesupplemental nut has end thrust when moved in a rotative direction aboutthe screw member, said end thrust member being in fixed relativerelation to the first mentioned nut member, means exerting a yieldingforce against the supplemental nut member in said rotative dircctionwhereby to exert a force against the screw member in a direction tomaintain its thread against one side of the thread of the firstmentioned nut member when the table, is propelled in the direction forclimb cutting, said force against the-screw member being exerted in thesame direction as the travel of the work table when climb cutting.

6. In a milling machine, the combination of a milling cutter, a work'support, a screw member and a nut member one of which is adapted to berotated in opposite directions to produce feed movement between themilling cutter and the work support in opposite directions, the millingcutterbeing rotated .in one dilLCtiOXl only for milling work fed inopposite directions for normal milling and climb milling, respectively,a supplemental nut on the screw member having an inclined face, a fixedmember havingan inclined face complemental to that of the supplementalnut, and means for imparting a force against the supplemental nutrotative about the screw member whcreby the action of the inclined faceof the supplemental nut against that of the screw member will exert aforce against and lengthwise of the screw member in a direction tomaintain its thread against one side of the thread of the firstmentioned nut member when climb milling, the direction of said forceagainst the screw m'tmber being the same as the direction of feedmovement when climb milling.

7. In a milling machine, the combination set forth in claim 6, in whichthe force exerted against the screw member is suiiicient to maintainsaid side of the screw member against said side of the nut member whentraversing or approaching the work with respect to the milling cutter inthe direction ofv the climb milling feed.

8. In a milling machine, in combination, a milling cutter, areciprocable work table, a rotary screw for reciprocating the table,means for rotating the screw in opposite directions, a fixed nut inwhich the screw operates, a supplemental nut on the screw having atoothed face, a rack member meshing with said toothed face, means urgingsaid rack member to impart rotative movement to the supplemental nut ina given direction, and a fixed cam face against which a cam face on thesupplemental nut acts under the influence of said nut rotating means,whereby to impart a" thrust against the screw in the same direction asthe thrust from the cutter when climb cutting.

9. A back lash remover for motion transmitting elements including ascrew, a fixed nut, and an auxiliary nut on the screw, and meansincluding a pressure wedge constantly exerting pressure axially betweenthe nuts, the angle or said wedge serving to cause the auxiliary nut totake up the play of the threads in both nutsand yield toirregularitiesof the screw thread, said pressure wedge providing anabutment resisflilz the thrust between the motion transmitting elementsfor either direction of motion transmission.

10. In combination, a screw, a nut therefor, means causing rotationbetween said screw and said nut, a supplemental nut for said screw,automatic means acting independently of the firstnamed means exertingrotative force upon said supplemental nut for changing the distancerelation between the said nuts, said automatic means including meanswhereby said rotative force acts in one direction for either directionof rotation of said first named means, and holding means resisting endthrust between said screw and said nuts in such changed distancerelation.

11. In combination, a screw, a nut therefor, means causing rotation inopposite directions between said screw and said nut, a supplemental nutthreaded to said screw, means exerting rotative force in one directiononly upon said supplemental nut, a cam element acted upon by said forcefor changing the axial distance between said nuts, and a cooperating camelement to resist end thrust acted on by said last-named means.

12. In means for feeding a machine element, the combination of a screw,a nut therefor, means for causing rotation between the screw and nut, asupplemental nut on the screw, helical means rotative about the screw,means cooperating with said helical means for causing the latter whenmoved rotatively to exert a force axially thereof causing the said nutand supplemental nut to be held against opposite sides of the screwthread to take up back-lash between the .said screw and nut for thetransmission of feed motion free from play, means acting on said helicalmeans to cause said force to be applied in one direction when thefirst-named means is operated for feeding in either one direction or theother, said helical means and said cooperating means being constructedand arranged to compensate by rotative advancement or retraction forvariances in the screw thread.

13. In a milling machine, feed mechanism for normal milling and climbmilling, including a screw and nut feed, means for causing rotationbetween said screw and nut, a supplemental nut on the screw, helicalmeans rotative about the screw, means cooperating with said helicalmeans for causing the latter when moved rotatively to exert a forceaxially thereof causing the said nut and supplemental nut to be heldagainst opposite sides of the screw thread to take up back lash betweenthe said screw and nut for the transmission of feed motion free fromplay, means acting on said helical means to cause said force to beapplied in one direction when the firstnamed means is operated forfeeding in either one direction for normal milling or-in the oppositedirection for climb milling, said helical means and said cooperatingmeans being constructed and arranged to compensate by rotativeadvancement or retraction for variances in the screw thread.

14. In a milling machine, mechanism for normal milling and climbmilling, including a screw and nut feed, means for causing rotationbetween the screw and nut to feed in one direction for normal millingand in the opposite direction for climb milling, a supplemental nut onthe screw, cam means including a movable cam element arranged to exertforce to maintain one of said nuts against one side of said thread andthe other nut against the opposite side of said thread to take up backlash in the screw and nut feed,

and means acting on said movable cam element for causing said force tobe exerted in one direction only when the first-mentioned means isoperated for causing said feed in either one direction or the other,said cam means being constructed and arranged so that said movable camelement will compensate by advancement or retraction during theapplication of said force for variances in the screw thread.

15. Motion transmitting mechanism including a screw and a pair of nutelements, means for causing rotation between the screw and nuts, meansincluding a cam element constructed and arranged to constantly exertpressure axially between the nuts to take up play between said nuts andthe screw, the angle of the cam element being such as to cause one ofthe nuts to yield to irregularities in the pitch of the screw thread,and including means whereby said cam element acts in one direction foreither direction of rotation 01' the first-named means.

16. In means for moving a machine element by relative rotation 01' ascrew and a nut, the combination of a screw, a nut therefor, means forcausing rotation between the screw and the nut, a supplemental nut onthe screw camming means including a movable camming element arranged toexert a force axially relatively between the nut and the supplementalnut tending to hold them against opposite sides of the screw thread totake up back-lash between said screw and nut for the transmission ofmotion to said machine element free from play, and means acting on saidmovable camming element to cause said force to be exerted in onedirection when the first-named means is operated for moving the machineelement in either one direction or the other.

17. In means for moving a machine element by relative rotation of ascrew and a nut, the combination of a screw, anut therefor, means forcausing rotation between the screw and the nut, a supplemental nut onthe screw, camming means including a movable camming element arranged toexert a force axially relatively between the nut and the supplementalnut tending to hold them against opposite sides of the screw thread totake up back-lash between said screw and nut for the transmission ofmotion to said machine element free from play, and means acting on saidmovable camming element to cause said force to be exerted in onedirection when the first-named means is operated for moving the machineelement in either one direction or the other, said means beingconstructed and arranged so that said movable camming element willcompensate by advancement or retraction for variances in the pitch ofthe screw thread.

18. A back-lash remover for motion transmitting elements including ascrew, a nut held against axial displacement, means for causing rotationbetween the nut and the screw, a supplemental nut on the screw,cooperating camming elements constructed and arranged to pro-.

duce a wedging action axially relatively between the nut and thesupplemental nut to take up play between said nuts and the screw thread,means acting through one of the camming elements to cause said wedgingaction to be exerted in one direction when the first-named means isoperated for transmitting motion in either one direction or the other,and said cooperating camming elements being constructed and arranged tocompensate in said wedging action between the nut and the supplementalnut for variances in the pitch of the screw thread.

19. A back-lash remover for transmitting motion to a machine element byrelative rotation of a screw and a nut in opposite directions, ineludinga supplemental nut on the screw, camming means constructed and arrangedto cooperate with said supplemental nut to exert a force axiallyrelatively between the nut and the 10 supplemental nut tending to holdthem against opposite sides of the screw thread to take up back-lashbetween said screw and nut tor the transmission of motion to saidmachine element tree from play, and means acting through said cammingmeans to cause said force to be exerted in one direction when thefirst-named means is operated for moving the machine element in eitherone direction or the other.

CERTIFICATE OF CORRECTION.

Patent No. 2,002,991. May 28, 1935.

CHARLES a. De VLIEG.

It is hereby certified that error appears in the heading to the printedspecification of the above numbered patent requiring correction asfollows: Line 6, for the words "Refiled for abandoned" read Continuationof; page 4, first column, line 72, claim 14, after "exert" insert thearticle a; and second column, line 26, claim 16, after "screw" insert acomma; and that the said Letters Patent should be read with thesecorrections therein that the same may conform to the record of the casein the Patent Office.

Signed and sealed this 10th day of September, A. D. 1935.

Les-l ie mm Acting Commissioner of Patents.

